At present, there are three coil layouts of a coreless type linear motor, respectively: non-overlapping concentrated winding, overlapping concentrated winding and printed circuit board. With reference to FIGS. 9 and 10 for a concentrated winding layout, a plurality of unit coils 10 are concentrated and arranged, wherein each unit coil stands for a phase U, V, W of the linear motor and matches the magnetic pole pitch of a permanent magnet 101 to produce a driving force. The difference of non-overlapping windings as shown in FIG. 9 and overlapping windings as shown in FIG. 10 resides on whether or not the windings between the unit coils are overlapped; and a printed circuit board layout method as shown in FIG. 11 forms a coil 102 on a printed circuit board 103 by using a printed circuit board manufacturing technology. Due to the limitations of the space and the number of windings of the coil, the printed circuit board layout method can be applied to the design for small driving forces only. Although the non-overlapping concentrated winding layout method can produce a larger driving force, yet there are spaces not used effectively in the hollow portion of the coil. The overlapping concentrated winding layout method can fill the space that cannot be used in the non-overlapping concentrated winding layout method, and thus the overlapping concentrated winding layout method is better than the printed circuit board layout method and the non-overlapping concentrated winding layout method and capable of maximizing the driving force in a minimal space.
There are different common overlapping concentrated winding layout methods. For instance, a unit coil layout as disclosed in U.S. Pat. No. 4,758,750 adopts three unit coils stacked and fixed to an insulating element to form a flat tri-phase unit coil module, and then a plurality of flat tri-phase unit coil modules are arranged and assembled into a linear motor coil assembly. If it is necessary to produce a larger driving force by the aforementioned method, more flat tri-phase unit coil modules will be required, and thus the weight of the linear motor coil assembly will be increased substantially, and the insufficient strength at the joint between the flat tri-phase unit coil modules will reduce the overall rigidity.
In view of the foregoing shortcomings, a coil layout method disclosed in WO 2004/017500 A1 improves over the unit coil overlapping method, wherein the unit coil includes two vertical action sides and two axial non-action sides to constitute a closed loop. After the unit coil are bent appropriately, the unit coils are stacked alternately on the axial non-action sides and arranged closely with each other in an axial direction to form a tri-phase unit coil module. Since the plurality of tri-phase unit coil modules can be stacked alternately in the axial direction and arranged into a coil assembly without having the issue of insufficient rigidity at the joint of the flat tri-phase unit coil modules, therefore the drawback of a heavy linear motor coil assembly can be overcome. The unit coil must have a larger number of windings to produce a larger driving force, and thus the thickness or the width of the unit coil will be increased, and the thicker unit coil will make the bending process more difficult. Furthermore, the thickness of a bent unit coil is at least 1.5 times of the original thickness of the unit coil in order to achieve the overlapping effect. When the linear motor coil assembly is assembled, each unit coil is connected in series-parallel, and the reserved space is provided for placing the connecting wires. Therefore, a larger space for the thickness is required at the position of the axial non-action side, and at least twice of the thickness of unit coil is added to the thickness of the reserved wire connection space to give the total thickness at the axial non-action side of the coil assembly. If the unit coil with a larger width is bent to the axial non-action side, the width will become the increase of the length of the coil, and a larger space for the increased length is required.
With reference to FIG. 12 for a common single unit coil 7 used for the overlapping to form a tri-phase unit coil module 31, the thickness of the axial non-action side of the formed unit coil 7 is equal to the sum of twice of T6 and the thickness T7 for the reserved space for the wire connection. However, the larger the thickness T6 of the formed unit coil 7, the more difficult is the formation, and the greater is the difference between the radii of internal bends R31, R33 and the radii of external bends R32, R34. The smaller radii of internal bends R31, R33 will result in a poor insulation.
In FIGS. 13(a) and 13(b), if the width of the unit coil 8 is larger, and the width is assumed to be W3, then the width of the coil will become the height W3 of the two rear axial non-action sides of the formed coil, and thus the total height of the coil will become larger, and the height of the linear motor coil assembly 3 as shown in FIG. 1 will increase.
In FIGS. 14(a) and 14(b), the sub-coil 9b is formed by a common winding method such as the vertical overlapping method, and thus its hollow portion 92 is not tapered but arranged vertically upward. In other words, the lengths L4 and L5 of the hollow portion of the coil are equal (L4=L5), such that after the coil 9b is bent and formed, the common formed sub-coil 9b′ as shown in FIG. 14(c) is tilted at the end of the axial non-action side 93′, since the length of internal sides of the formed coil 9b′ are equal (L4′=L5′), and the length of the external side L5′ includes a larger radius of bend R5′, and the length of the internal side L4′ includes a smaller radius of bend R4′. As a result, the external side of the axial non-action side 93′ of the formed coil 9b′ is tapered to a greater extent than the internal side as shown in FIG. 14(d). The required thickness of the linear motor coil assembly 3 is increased due to the tilted axial non-action side 93′.
With reference to FIG. 15 for a method of connecting wires between the unit coils of a common coil assembly, a method of connecting equivalent circuits in series is adopted to produce a larger driving force as shown in FIG. 15(a), or a method of connecting equivalent circuits in parallel is adopted to provide a higher speed as shown in FIG. 15(b), or a method of connecting equivalent circuits in series-parallel is adopted to produce a linear motor with different characteristics as shown in FIG. 15(c). However, these wire connection methods are applicable for the wire connection between unit coils only. Other methods must be used to achieve the expected characteristics of the linear motor.